Advertisements (like many things) are a matter of personal preference. Some people found the Taco Bell dog funny and endearing. Other people disliked the Taco Bell dog commercials. As time passed, some people moved from the first camp into the second. To a viewer of commercials, good commercials can have a great effect: I like that commercial, so I'm more inclined to buy/use that product. It has been largely overlooked that bad commercials can have the opposite effect. Viewers will avoid products that are represented by bad commercials. Or, similarly as illustrated above, repetition can cause viewers to start avoiding the product over time. In the case of certain events (watching college basketball all day on a Saturday, for example), the same commercials are shown repeatedly, causing even a good commercial to have the effect of a bad commercial.
Advertisers make advertisements to appeal to viewers to entice them to buy their product(s). Frequently, a bad advertisement will turn a viewer off of a product, and repetition of a bad advertisement can make a viewer avoid a product altogether. Over-repetition of a good advertisement can have an adverse effect as well.